I have a 2011 Cadillac DTS and the air level ride continues to run whether the key is on or not. Only way it will quit is if I pull the fuse .

You have a leak in the system somewhere, air line more than likely.

Is your car lower in the morning after letting it sit overnight?

could also be a bad sensor too.

Where is the sensor so I can check it?

I do not know where a sensor would be. I believe 90% it is going to be an air line that rubbed threw somewhere and caused a leak, or a bad air bag.

The sensor your looking for is your height control sensor, it should be on either your passenger or drivers rear control arm, sometimes they get stuck either up or down, depending the wear

If I were you, I'd eliminate all small possible leaks or line cracks, that sensor is a couple hundred at most parts stores unless you find a cheap one online